avif-decoder: Convert directly to RGBA

e3f81a4 introduced a byte swap
conversion from BGRA to RGBA, which can be eliminated if we ask dcp to
convert directly to RGBA.

src/codecs/avif/decoder.rs

@@ -112,7 +112,7 @@ impl<'a, R: 'a + Read> ImageDecoder<'a> for AvifDecoder<R> {
                 num_planes: 3,
             };
             let dst_format = dcp::ImageFormat {
-                pixel_format: dcp::PixelFormat::Bgra,
+                pixel_format: dcp::PixelFormat::Rgba,
                 color_space: dcp::ColorSpace::Lrgb,
                 num_planes: 1,
             };
@@ -160,11 +160,6 @@ impl<'a, R: 'a + Read> ImageDecoder<'a> for AvifDecoder<R> {
             }
         }
 
-        // Convert Bgra to Rgba
-        for chunk in buf.chunks_exact_mut(4) {
-            chunk.swap(0, 2);
-        }
-
         Ok(())
     }
 }